Scanning force microscope and method for beam detection and alignment

ABSTRACT

A scanning force microscope ( 10 ) sometimes referred to as an atomic force microscope employs a laser ( 32 ) and a cantilever ( 28 ) which move proportionally to a moving reference frame ( 64 ). A fixed reference frame ( 11 ) contains optical components. A scanning mechanism creates relative movement between the fixed and moving reference frames. An optical assembly ( 114 ) is included which comprises at least one optical device in the fixed reference frame. The optical assembly permits initial alignment of the laser beam onto the cantilever and also permit the laser beam to follow the moving cantilever.

This is a continuation of application Ser. No. 08/950,030, filed Oct.14, 1997, which is incorporated by reference herein, now U.S. Pat. No.5,861,550.

BACKGROUND

1. Field of the invention

This invention relates to scanning force microscopes, sometimes referredto as atomic force microscopes, using light beam detection schemes.

2. Description of Prior Art

Conventional optical microscopes used to observe the surface features ofmaterials begin to lose resolution when the dimensions of the surfacefeatures approach one half the wavelength of visible light. Alternatetypes of microscopes have been developed to overcome this limit.Confocal microscopes, for example, can improve on conventional opticallimits. Scanning electron microscopes image small surface features bythe use of energized electrons that have wavelengths shorter thanphotons. However, many of these alternate techniques have limits oftheir own and may have other disadvantages in implementation such as aneed to place the sample in a vacuum chamber.

A new class of microscopes overcomes the resolution limits of previoustechniques in a fairly simple manner. Microscopes in this class arereferred to as probe microscopes. The topographical version of these newmicroscopes uses a fine pointed stylus to interact with some parameterof the sample surface. A scanning mechanism creates relative motionbetween the stylus and the sample surface. When a measurement is made ofthis interaction, the surface topography of the sample can be imagedwith height as well as lateral detail. One of the more commerciallysuccessful microscopes in this class is the scanning force microscopealso referred to as a scanning force microscope. Sample features otherthan topography can be measured with probe microscopes. For example,when measuring the interaction of a magnetic probe with the magneticfields of the sample, an image of the magnetic domains of the sample canbe created.

For topographical operation the stylus is mounted orthogonally to thelonger dimension of a cantilever such that the cantilever acts as abending lever. A cantilever is a lever with a constrained end and a freeend. The stylus is mounted near the free end. The cantilever deflectsdue to the force applied to the stylus as the stylus interacts with thesample surface. The combination of a stylus and cantilever are referredto as a probe assembly. The cantilever has a very weak spring constantand may noticeably deflect when a force as small as one nanonewton isapplied to its free end. A detection mechanism provides a signal to afeedback loop when the cantilever deflects. When relative lateral motionexists between the stylus and the sample surface, the changingtopography under the stylus creates a force on the stylus which thestylus transmits to the free end of the cantilever. This results in aslight change in the angle of the free end of the cantilever. A lateraldrive mechanism creates relative lateral motion between the stylus andsample. The feedback loop controls a vertical drive mechanism whichmoves the fixed end of the cantilever toward and away from the samplesurface. Consequently, the free end of the cantilever surface is held ata nearly constant bend angle. The lateral and vertical drive mechanismsare referred to as a scanning mechanism.

By measuring the vertical drive signal and the lateral position of thestylus over the sample, a matrix of x, y and z values may be created.This matrix describes the surface topography of the sample.

The surface of the cantilever is at least partially reflecting. Thedeflection of the free end of the cantilever is measured by directing alaser beam onto the free end, and by measuring the position of thereflected beam. The stylus is mounted on the surface opposite thereflecting surface of the cantilever. Further, an array of two or morelight-sensitive devices may be used to detect the position of thereflected beam. These devices then produce electrical signals which arerelated to the cantilever deflection. The difference of the two signalsis proportional to the amount of the cantilever deflection in onedirection. Four light-sensitive devices arrayed in a quadrant canmeasure the amount of cantilever deflection in two orthogonaldirections. The vertical drive mechanism receives signals processed fromthe output of the light-sensitive devices. This creates the feedbackloop that controls the bend angle of the cantilever.

Prior art devices constructed as described above are shown in U.S. Pat.No. 4,935,634 to Hansma et al, and U.S. Pat. No. 5,144,833 to Amer et.al. These prior art devices move the sample laterally and verticallyunder a stationary stylus while detecting the cantilever deflection withthe laser beam apparatus described above. This method has a disadvantagestemming from the limited force capability of the lateral and verticaldrive mechanisms. The sample mass may be large compared to the forcecreated by the drive mechanisms. In such cases the sample may eithermove very slowly or not move at all under the stylus.

Prior art microscopes described in U.S. Pat. No. 5,481,908 and itscontinuation U.S. Pat. No. 5,625,142 to Gamble maintain a fixed sampleand move the laser, the cantilever, and all of the associated mechanismsthat are necessary to make initial adjustment of the laser beam. Sincethe laser moves with the cantilever, the laser beam follows the motionof the cantilever during scanning. The mass associated with moving partof such microscopes limits the speed at which the image data can betaken.

Other prior art microscopes attempt to overcome the disadvantage ofmoving the sample by using an interferometric method to track a movingcantilever. These microscopes are described in U.S. Pat. No. 5,025,658and its continuation U.S. Pat. No. 5,189,906 to Elings et al. Further,prior art microscopes use moving beam steering optics with a stationarylaser source as described in U.S. Pat. No. 5,524,479 which is acontinuation of U.S. Pat. No. 5,388,452 to Harp and Ray and in U.S. Pat.No. 5,463,897 with associated continuation U.S. Pat. No. 5,560,244 toPrater et al as well as U.S. Pat. No. 5,440,920 and its continuationU.S. Pat. No. 5,587,523 to Jung et. al. These techniques employ a fixedposition laser and moving optical elements. The optical elements movewith the moving probe assembly. The result is a lateral redirecting ofthe laser beam which then follows the moving surface of the cantilever.

These systems must move optical components with the cantilever. Thisadds mass to the moving part of the system. These systems also positionthe laser in a location above the cantilever. This position may precludesimultaneous optimum optical viewing from positions above the cantileverand sample. The lateral and vertical drive mechanisms must accommodatethe potentially significant added mass of the moving optical devices byproviding additional force. The result is a significant limit to thevelocity of the stylus over the sample. In addition, if one wishes tooptically observe the probe assembly from certain angles it may benecessary to place additional mirrors or other optical devices on themoving part of the microscope. Further, mechanisms often are needed toadjust the laser over a range of angles, in order to initially bring thebeam onto the reflecting surface of the cantilever.

In probe microscopes it is often necessary to change the probe assemblyas the result of a blunted stylus. This is caused either by wear or bysmall particles which become attached to the stylus as it scans over thesample. Also the stylus may break. When the probe assembly is replaced,the replacement assembly often is not in exactly the same positionrelative to the laser and associated optical assemblies. Consequently,the laser beam angle normally must be adjusted to restore the beam toits proper position on the reflecting surface of the cantilever. Inprior art microscopes the mass of the adjustment mechanisms adds to themoving portion of the microscope. Other alternate prior art techniquesattach devices to the scanning mechanism which adjust the probelaterally. The scanning mechanism often consist of thin walledpiezoelectric tubes which are quite fragile. The operator may apply toomuch force when adjusting the probe lateral adjustment mechanism thusdamaging or breaking the tube.

OBJECTS AND ADVANTAGES

The present invention offers novel advantages over the prior art in thefollowing respects:

(a) the mass of the moving portion of the microscope is reduced;

(b) the laser beam may be adjusted, such that it illuminates the surfaceof the cantilever, by linkages which are not physically connected tofragile moving parts such as the lateral and vertical drive mechanism;

(c) the laser beam adjustment is simple and the method is easilyimplemented;

(d) visual access to the probe assembly is improved; and

(e) the laser beam tracks the motion of the probe assembly with minimalerror.

SUMMARY OF THE INVENTION

In my scanning force microscope a low mass laser is mounted in themoving frame of reference of the cantilever and stylus. A novel opticalsystem is employed with components mounted in a moving frame ofreference and in a fixed frame of reference. This allows initialadjustment of the laser beam onto the cantilever while allowing the beamto track the cantilever during scanning. It also maintains low mass forthe moving part of the microscope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a scanning force microscope employing a first embodiment ofthe invention in which a laser and probe are in a moving frame ofreference. An optical assembly is in a fixed frame of reference butallows adjustment of the laser beam.

FIG. 1A describes a coupling assembly used in the invention.

FIG. 1B shows a typical probe assembly.

FIG. 1C schematically shows beam paths for an uncorrected beam.

FIG. 1D schematically shows beam paths for a corrected beam.

FIG. 1E schematically shows beam paths for a beam corrected with asecond compensation lens.

FIG. 2 shows a scanning force microscope employing a second embodimentof the invention in which the laser is mounted laterally.

FIG. 3 shows a scanning force microscope employing a third embodiment ofthe invention in which the laser is placed at the lower end of thevertical driver.

FIG. 4 shows a scanning force microscope employing a fourth embodimentof the invention employing a pentagon prism.

FIG. 5 shows a scanning force microscope employing a fifth embodiment ofthe invention using an adjustable spherical mirror.

DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE DRAWINGS

A preferred embodiment of the invention is given in FIG. 1. A microscope10 has a fixed reference frame 11. A scanner mount 12 attaches a lateraldriver 14 to fixed reference frame 11. Lateral driver 14 may be in theform of a piezoelectric tube with electrodes (not shown). The free endof lateral driver 14 appears to rotate around a mechanical pivot 16.Mechanical pivot 16 is located approximately at the mid point betweenthe fixed and free end of lateral driver 14. A laser coupler assembly 18couples the free end of lateral driver 14 to the upper end of a verticaldriver 22 and also carries a laser 32 in the x and y directions. Laser32 has a focusing lens 34 which produces a converging beam of light witha first segment 36.

Vertical driver 22 may be a piezoelectric tube with electrodes (notshown). A probe assembly holder 24 is connected to the lower end ofvertical driver 22 and supports a probe assembly 26. First beam segment36 impinges on a first fixed mirror 38 resulting in a second beamsegment 40. Second beam segment 40 impinges on a lateral adjustablemirror 44 which is attached to a lateral adjustable mirror support 46.Mirror support 46 pivots about a lateral adjustable mirror axis 48.Lateral adjustable mirror 44 and mirror support 46 compose a lateraladjustable mirror assembly 42. A third beam segment 52 extends through afixed compensation lens 54 and impinges on a vertical adjustable mirror58.

Mirror 58 is supported on a vertical adjustable mirror support 60 whichrotates about a vertical adjustable mirror axis 62. Mirror 58 and mirrorsupport 60 compose a vertical adjustable mirror assembly 56. A fourthbeam segment 66 reflects from mirror 58 and impinges on a second fixedmirror 68 resulting in a fifth beam segment 70. Beam segment 70 passesthrough a probe holder throughbore 74 and then impinges on a cantilever28. A stylus 30 reacts to forces generated by the proximity of a sample50 and further transmits the forces to cantilever 28. Cantilever 28,stylus 30 and a die 112 shown in FIG. 1B form probe assembly 26. Themotion of the lower end of vertical driver 22 creates a moving frame ofreference 64 relative to fixed reference frame 11. All opticalcomponents in either fixed reference frame 11 or in moving referenceframe 64 and in the light path between laser 32 and cantilever 28 createan optical assembly 114. A sixth beam segment 72 reflects fromcantilever 28 and passes through a beam sizing lens 76 and then impingeseither on a first photodiode 78 or a second photodiode 80 or both.Electrical signals from first and second photodiodes 78 and 80 arerouted to a difference amplifier 82.

FIG. 1A shows laser coupler assembly 18 which consists of a laser holder20 and laser 32 which is inserted into a coupler throughbore 84. Lasercoupler assembly 18 then couples lateral driver 14 and vertical driver22 together to provide for proportional motion between laser 32 andcantilever 28.

FIG. 1B shows probe assembly 26 with die 112 which supports cantilever28. Cantilever 28 has an upper surface 110 which is at least partiallyreflecting. Stylus 30 is supported on the surface of cantilever 28opposite upper surface 110. Cantilever 28 has a weak spring constant andwill deflect measurably with as little as one nanonewton of forceapplied to stylus 30.

FIG. 1C diagrams, in the absence of any compensating optical devices, anuncorrected light beam path 96. During scanning, probe assembly 26rotates through an angle θ which is typically less than 0.2 degrees. Forsuch small angles of θ, probe assembly 26 rotates approximately aroundmechanical pivot 16 to an alternate position shown as a rotated probeassembly 26′. Probe assembly 26 is at the physical length of a centerpath 88 from mechanical pivot 16. The light following center path 88reflects from probe assembly 26 along a center reflected path 92. Arotated center light path 94 shows the desired path of the light beamfor rotated probe assembly 26′. Uncorrected light beam path 96 alsorotates through angle θ, however, because the optical path is longer byan extended distance 90, path 96 rotates around an optical pivot 86. Theresult is that the light beam following path 96 misses rotated probeassembly 26′ and is not reflected back to photodiodes 78 and 80.

FIG. 1D shows fixed compensation lens 54 in uncorrected light beam path96. Now, the beam is refracted towards rotated probe assembly 26′ alonga corrected beam path 100. The reflected beam from probe assembly 26follows center reflected path 92 and impinges near a center position onphotodiodes 78 and 80. However, the reflection of the light beam oncorrected path 100 results in a light beam following a rotated reflectedbeam path 98. Path 98 impinges on photodiodes 78 and 80 at a slightlydifferent location from the beam on center reflected path 92. Thelocation error in position may be corrected in software since the erroris a predictable function of the position of assembly 26′ as it rotatesin the x and y directions. The error is minimal because in actualpractice the angle θ is typically less than 0.2 degrees. The focallength and position of compensation lens 54 is calculated using itsposition relative to optical pivot 86 and standard formulas which relatethe focal, image and object distances of lenses.

FIG. 1E shows a method of compensating for angular errors. Probeassembly 26 rotates to a position shown by rotated probe assembly 26′approximately around mechanical pivot 16. However, the light followingpath 96 rotates around optical pivot 86. Compensation lens 54 refractsbeam path 96 to a first corrected light beam path 102. A secondcompensation lens 108 refracts first corrected light beam path 102 to asecond corrected light beam path 104. Path 104 appears to emanate fromand pivot around mechanical pivot 16. For small angles of θ, the lightreflected from assembly 26′ follows a reflected corrected beam path 106.Path 106 starts at rotated probe assembly 26′ and arrives at nearly thesame position on photodiodes 78 and 80 as the light which follows path92.

FIG. 2 shows laser 32 and focusing lens 34 attached to a laser couplermirror holder 122 which further carries a diverting mirror 116. Laser32, diverting mirror 116 and holder 122 compose a laser coupler andmirror assembly 120. A diverted beam segment 118 passes through fixedcompensation lens 54 and second compensation lens 108. Diverted beamsegment 118 is reflected from mirror assembly 56 and then from lateraladjustable mirror assembly 42.

FIG. 3 shows laser 32 and focusing lens 34 attached to a laser mirrorprobe holder 128 which is attached to the lower end of vertical driver22. A coupler 124 connects lateral driver 14 to vertical driver 22.

FIG. 4 shows laser 32 and focusing lens 34 attached to a laser probeholder 132. A laser initial beam path 126 leads to a pentagon prism 130and then is directed to mirror assembly 56 and then to lateraladjustable mirror assembly 42.

FIG. 5 shows beam path 126 impinging on pentagon prism 130 andsubsequently impinging on a spherical mirror 136. Laser 32, probeassembly 26, and a probe mirror 144 are supported by an alternate holder134. Spherical mirror 136 is connected to a spherical mirror support 138which can be rotated about a vertical axis 140 and a lateral axis 142.The light following a second beam path 146 then is reflected towardprobe mirror 144 and subsequently to probe assembly 26. Sample 50 isimmersed in a fluid 200 retained by a conventional container 202.

OPERATION OF THE INVENTION

Referring to FIG. 1 assists in understanding the operation of the firstembodiment of the invention. For small angles of rotation, lateraldriver 14 causes rotation of all parts and assemblies attached to itsfree end to rotate about mechanical pivot 16. Consequently, laser 32 andfirst beam segment 36 also rotate substantially about mechanical pivot16. Lens 36 causes the light emitted from laser 32 to converge toapproximately a point at cantilever 28. To an observer positioned to theright of mirror 38, beam segment 40 appears as if it were coming fromthe opposite or left side of mirror 38. The same is true for an observerviewing each reflected beam, i.e. the beam appears to come from theopposite side of each mirror as the beam continues on to mirror 44,mirror 58 and second fixed mirror 68.

Lateral and vertical adjustable mirrors 44 and 58 permit the beam to beadjusted such that it impinges on cantilever 28 before scanning starts.Compensation lens 54 redirects segment 52 causing it to followcantilever 28 despite the difference between the optical path length andthe mechanical path length as was seen in the description of FIG. 1D. Itis important to note that compensation lens 54 also has an effect on thefocus of beam segment 52. When calculating the focal length of focusinglens 34 this effect must be considered. The result is that beam segment70 tracks the movement of cantilever 28 during scanning . Beam segment72 reflects off cantilever 28 and continues through beam sizing lens 76to impinge on photodiodes 78 and 80. The diameter of beam segment 72,when it reaches photodiodes 78 and 80, is increased or decreased byoptional beam sizing lens 76 to a value which matches the physical sizeof photodiodes 78 and 80. Standard formulas relating the image, object,and focal length of lenses are used to calculated the focal length andposition of lens 76. The focal lengths and positions of lenses 54 and 76are calculated to sufficient accuracy using the thin lens formula:${\frac{1}{f} = {\frac{1}{s} + \frac{1}{s^{\prime}}}},$

where ƒ is the focal length of the lens, s is the distance from theobject to the lens, and s′ is the distance from the lens to the image.The appropriate sign conventions must be followed when making thecalculations.

As stylus 30 encounters different elevations on the surface of sample 50the position of the reflected beam on the photodiodes will change.Electrical signals from photodiodes 78 and 80 are subtracted andamplified by difference amplifier 82. In response to feedback signalsprocessed from the output of amplifier 82, vertical driver 22 expandsand contracts in the z direction to move probe assembly 26 and probeassembly holder 24 vertically. Cantilever 28 bends under the influenceof changes in the expansions and contractions of vertical driver 22.Cantilever 28, therefore, holds a nearly constant force on stylus 30 asthe topographical features of sample 50 as pass under stylus 30.

In FIG. 2 the operation is similar that in FIG. 1 except that laser 32is coupled to diverting mirror 116. Both laser 32 and mirror 116 rotateabout mechanical pivot 16. This eliminates the need for first and secondfixed mirrors 38 and 68 shown in FIG. 1. The positions of lenses 54 and108 are determined by their selected focal lengths and the distance ofthe optical path taken by the light beam. Standard formulas forcalculating focal, object and image distances for multiple lens systemscan be used. Lenses 54 and 108 can be placed in the beam path betweenmirror assemblies 56 and 42 or between mirror assembly 42 and probeassembly 26. Before scanning begins the light beam is adjusted ontocantilever 28. During scanning, lenses 54 and 108 will cause the beamwill follow cantilever 28 as it rotates about mechanical pivot 16.

FIG. 3 shows a further alternate method. Holder 128 supports laser 32.Diverting mirror 116 rotates with holder 128. Light from laser 32 isrouted to cantilever 28 by refraction at lens 54 and by reflection frommirror assemblies 42 and 56. The beam reflects from cantilever 28 andimpinges on photodiodes 78 and 80.

FIG. 4 shows how pentagon prism 130 is used to eliminate fixed mirrors38 and 68 shown in FIG. 1. Prism 130 also eliminates diverting mirror116 shown in FIG. 2. A pentagon prism has the property that it does notpervert the image as does a single plane mirror. Lens 54 causes the beamto follow cantilever 28 as it rotates around pivot 16. The reflectedbeam impinges on photodiodes 78 and 80.

FIG. 5 eliminates compensation lens 54 and the adjustable mirrors 44 and58 of FIG. 1 by interposing adjustable spherical mirror 136. Mirror 136is adjustable around vertical axis 140 and lateral axis 142. Probemirror 144 rotates about pivot 16. Spherical mirror 136 compensates forthe nearly spherical rotation of laser 32, probe mirror 144 and probeassembly 26. Pentagon prism 130 is used for conveniently redirectingpath 126. For a generalized spherical mirror the radius of curvature isfound from standard formulas relating the radius, image distance, andobject distance. For light rays with an angle of approximately 0.2degree or less, the radius of curvature is calculated with sufficientaccuracy using the following formula:${\frac{2}{R} = {\frac{1}{s} + \frac{1}{s^{\prime}}}},$

where R is the radius of curvature of a spherical mirror, s is thedistance from the object to the mirror, and s′ is the distance from themirror to the image. The appropriate sign conventions must be followedwhen making the calculations.

SUMMARY, RAMIFICATIONS, AND SCOPE

With my scanning force microscope it is possible to adjust the laserbeam onto the cantilever without mechanical linkages to either thelateral or vertical driver nor to any part that moves with the lateralor vertical driver. The light beam continues to track the motion of thecantilever as it scans over the surface of the sample. Further, by usinglow mass components the mass of the moving elements is reduced and thesystem is able to scan at a faster rate. The implementation isuncomplicated and straight forward.

While the description given above is quite specific and detailed itshould not be considered to limit the scope of the invention but shouldinstead be considered as only describing some examples of the invention.There are many alternate variations of the invention. For example, thelenses shown are double concave and double convex. They can be pianoconvex, piano concave, achromatic, cylinder, meniscus or graded indexlenses. Roof prisms, porro prisms and right angle prisms can besubstituted or added to the light beam path. Optical wedges can be usedto refract the beam. The plane mirrors can have slightly curved surfacessuch that they act similar to the compensation lenses shown. Further,optical fibers can be used to redirect the light beam.

The methods for rotating the adjustable fixed frame lenses and mirrorscan employ lead screws, differential thread lead screws, orpiezo-actuators or combinations of these.

The scanning mechanism can take many forms. The vertical and lateraldrivers can be piezoelectric blocks, stacks, tubes or bimorphs. Thevertical and lateral drivers can be actuated by piezoelectric devices orby magnetic or magnetostrictive devices. The vertical and lateraldrivers can be combined into one device such as a single piezoelectrictube that can create relative motion in the x, y and z direction withrespect to the sample surface.

The light source is a device capable of generating light and may be alaser, a light emitting diode, or an incandescent light source. Thelight detectors in the examples are photodiodes, but there are othertypes of devices such as phototransistors that can detect light. If anarray of four or more light detecting devices is used, the lateralmotion of the beam as well as the vertical motion can be detected.

The output signal from the difference amplifier can be processed to forma signal which actuates a motor which in turn drives the adjustablemirror assemblies mounted in the fixed reference frame. This makespossible automatic adjustment of the adjustable assemblies.

The scanning force microscope described here can operate with the samplesubmerged in fluids. Further, the microscope can operate by oscillatingthe cantilever and detecting some parameter of the oscillation such asthe amplitude, frequency, or phase change in the electrical outputsignals as the oscillating cantilever approaches the proximity of thesample surface. The oscillating cantilever may actually come intointermittent contact with the sample surface.

In the examples given a stylus is used to create a bending action of thecantilever. However, other types of probes, such as magnetic probes, canbe used to bend the cantilever.

Thus the scope of the invention should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

I claim:
 1. A scanning force microscope comprising: (a) a fixedreference frame; (b) a moving reference frame; (c) scanning means forcreating relative motion between said fixed reference frame and saidmoving reference frame; (d) a light source mounted in said movingreference frame adapted to provide a light beam; (e) an optical assemblymounted in said fixed reference frame, adapted to receive and transmitsaid light beam, containing at least one device selected from the groupconsisting of lenses, mirrors, and prisms; (f) a cantilever mounted insaid moving reference frame and adapted to receive said transmittedlight beam; (g) a light beam position detector adapted to receive lightreflected from said cantilever.
 2. The scanning force microscope ofclaim 1 where said scanning means consists of at least one piezoelectrictube.
 3. The scanning force microscope of claim 1 further comprisingmeans for adjusting said optical assembly.
 4. The scanning forcemicroscope of claim 1 further including a lens which changes thediameter of a beam after said beam is at least partially reflected fromsaid cantilever.
 5. The scanning force microscope of claim 1 where saidlight beam position detector includes at least two light detectingdevices.
 6. The scanning force microscope of claim 1 where saidcantilever is immersed in a fluid during scanning.
 7. The scanning forcemicroscope of claim 1 further including means for oscillating saidcantilever and means for detecting a change in a parameter ofoscillations in said light beam where said light beam is at leastpartially reflected off said cantilever.
 8. A method of imaging a samplewith a scanning force microscope comprising the steps of: (a) providinga cantilever and a light source in a first reference frame; (b)providing an optical assembly in a second reference frame; (c) mountingsaid sample in said second reference frame; (d) providing relativemovement between said first reference frame and said second referenceframe; (e) directing a beam from said light source through said opticalassembly and on to said cantilever; and (f) detecting bending of saidcantilever.
 9. The method of claim 8 further comprising the steps of:(a) oscillating said cantilever; (b) detecting a change in a parameterof oscillation of said cantilever as said cantilever is influenced bysaid sample; and (c) processing said parameter of oscillation to createan image of said sample.
 10. A scanning force microscope including acantilever and a light source mounted in first reference frame and anoptical assembly adapted to direct light from the light source to thecantilever, the improvement comprising: a second reference frame adaptedfor motion relative to the first reference frame and in which theoptical assembly is positioned.
 11. The scanning force microscope ofclaim 10 where said light source is a laser.
 12. The scanning forcemicroscope of claim 10 where relative motion between said firstreference frame and said second reference frame is created by at leastone piezoelectric device.
 13. The scanning force microscope of claim 10where said cantilever deflects as a result of the magnetic fields ofsaid sample.
 14. The scanning force microscope of claim 10 where saidoptical assembly includes at least one adjustable optical component. 15.The scanning force microscope of claim 10 where said optical assemblyincludes at least one mirror with a curved surface.
 16. The scanningforce microscope of claim 10 where said cantilever supports a stylus andsaid stylus intermittently contacts a sample surface.
 17. The scanningforce microscope of claim 10 where said optical assembly comprises atleast one prism.